There is known an apparatus for lifting a liquid from a well comprising a housing formed by a pipe string run into the well. This housing accommodates an actuator in the form of plunger having a non-return valve. The upper part of the housing overlying the plunger communicates through selector valves with an intake line. The plunger is capable of reciprocating inside the pipe for which purpose it is connected through a flexible pull member with a drum the shaft of which is kinematically linked with the shaft of an electric motor (cf., e.g., USSR Inventor's Certificate No. 1,084,419 published in Russian in the Bulletin "Discoveries, Inventions, Industrial Designs, Trademarks" Apr. 7, 1984).
One inherent disadvantage of the above apparatus is failure to deliver a relatively large quantity of the fluid medium with one stroke of the plunger to a relatively long distance, since reliable sealing of the plunger with respect to the housing is virtually impossible. To ensure a high degree of such sealing, the inside surface of the string of pipes needs precise machining, which makes their fabrication too expensive. This prior art apparatus is therefore not sufficiently reliable or efficient, and features a rather short service life.